Since the introduction of chlorpromazine into clinical practice in the 1950's, neuroleptic (or antipsychotic) therapy has provided the most common form of treatment for schizophrenia; these drugs are also frequently prescribed in the institutionalized mentally retarded and institutionalized aged residents. Although neuroleptics are effective in alleviating the symptoms of schizophrenia and managing some inappropriate behaviors in the mentally retarded, their use is limited by the development of deleterious behavioral and physiological side effects. In order to better predict potential deficits in learning, memory and other intellectual functions associated with these drugs, the prototypical neuroleptics chlorpromazine and haloperidol have been examined extensively in nonhuman experimental models. However, specific information concerning the behavioral effects of the newer neuroleptic drugs in these models are virtually nonexistent. The purpose of the present investigation is to examine the acute behavioral effects of the neuroleptic drugs clozapine, sulpiride, thiothixene, and molindone, and compare their effects with those of chlorpromazine and haloperidol. This will be accomplished by examining the dose-effect relations for these drugs in pigeons responding under a delayed matching-to- sample and fixed-consecutive-number procedure. The former procedure provides a sensitive assay of the ability of drugs to affect conditional discriminations and memory, while latter has been effectively employed to evaluate the control by external stimulus conditions as a determinant of drug effects. Since neuroleptic drugs often display different behavioral and pharmacological activities, examination of the neuroleptics under these procedures may provide valuable insight into their behavioral effects and facilitate the search for behavioral techniques that can be used for the screening of neuroleptic agents with minimal behavioral side effects. Moreover, by providing correlations between the potencies of these drugs for altering rate and accuracy of responding with published reports of their affinities at various receptor sites, the present investigation will help provide a framework for the identification of the biochemical correlates of these neuroleptic-induced behavioral effects.